Well sealing via thermite reactions

ABSTRACT

A platform is formed in a well below a target plug zone by lowering a thermite reaction charge into the well and igniting it, whereby the products of the reaction are allowed to cool and expand to form a platform or support in the well. A main thermite reaction charge is placed above the platform and ignited to form a main sealing plug for the well. In some embodiments an upper plug is formed by igniting an upper thermite reaction charge above the main thermite reaction charge. The upper plug confines the products of ignition of the main thermite reaction charge.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 14/168,877, filed Jan. 30, 2014, the content of which isincorporated by reference into the present application.

BACKGROUND

This invention relates to methods for sealing a well using a thermitereaction charge placed or lowered into the well. The invention hasremedial and sealing applications for wells used in oil and natural gasproduction, as well as in other applications including sealing of wellsused for underground storage of nuclear waste, sequestration of CO₂, andthe like.

As used in this document, the term “thermite reaction” is intended torefer to a broad class of chemical reactions which can be defined as anexothermic reaction which involves a metal reacting with a metallic or anon-metallic oxide to form a more stable oxide and the correspondingmetal or non-metal of the reactant oxide. This is a form ofoxidation-reduction reaction which can be written in a general form as:

M+AO→MO+A+ΔH

where M is a metal or an alloy (typically, but not necessarily Aluminum)and A is either a metal or a non-metal, MO and AO are theircorresponding oxides, and ΔH is the heat generated by the reaction.Commonly, AO is one of the species of Iron Oxide, such as Fe₂O₃ orFe₃O₄. A typical thermite reaction is of the form 2Al+Fe₂O₃→2 Fe+Al₂O₃.The reaction produces a great deal of heat per unit of mass, and canattain a reaction temperature of approximately 3,000° C.

Thermite reactions have many uses, including welding, pyrotechnics,synthesis and processing of materials, and military applications.Background information on thermite reactions is described in the reviewarticle of Wang et al., Thermite reactions: their utilization forsynthesis and processing of materials, J. Materials Science 28 (1993)pp. 3693-3708; and in Fisher et al., A survey of combustible metals,thermites and intermetallics for pyrotechnic applications, presented atthe 32^(nd) AIAA/ASME/SE/ASEE Joint Propulsion Conference, Lake BuenaVista, Fla., Jul. 1-3, 1996. Additional background information is foundin Orru et al., Self-propagating thermite reactions: effect of aluminaand silica in the starting mixture on the structure of the finalproducts, Metallurgical Science and Technology 15 (1)(1997) pp. 31-38.The entire content of the Wang et al., Fisher et al. and Orru et al.articles is incorporated by reference herein.

Thermite reactions have also been proposed for well sealing application,see published PCT application WO 2013/133583 and US patent applicationpublication 2006/0144591. See also U.S. Pat. No. 6,923,263. Thermiteshave been applied in the drilling industry for blowout prevention (U.S.Pat. No. 5,159,983), explosive sealing of casing perforations (U.S. Pat.No. 5,613,557), gas generation for downhole tool actuation (U.S. Pat.No. 6,925,937), well perforation and hydrofracturing (US patentapplication publication 2011/0146519) and downhole bonding of metalmembers (US patent application publication 2012/0255742). Many otherpatents exist for welding and demolition with thermite in above groundapplications, but these are not considered relevant to borehole sealapplications.

The basic concept of emplacing thermite charges into a well to performsealing and structural roles is depicted in FIGS. 1A-1C. Referring toFIG. 1A, a well 100 (shown in cross-section) defined by the inner wallsof a formation 1 has a platform 2 in the form of a backfill or bridgeplug inserted into the well. A thermite charge 4, typically a compressedblock consisting of a mixture of a metal fuel material (such as aluminumpowder) and a metal oxide (such as iron oxide powder) is lowered to aposition in the well with some form of rigid platform 2 (such as abridge plug) supporting it. The platform 2 can be either granularbackfill material, cement, or a mechanical plug (bridge plug) protectedby an insulating material (not shown) on its upper surface. The thermitecharge 4 is then ignited by an electrical means, shown as igniter 3. Theigniter can be located on the bottom, in the interior, or on the top ofthe thermite charge. As shown in FIG. 1B, after the igniter 3 isactivated, the thermite charge 4 burns in place as a self-sustainingexothermic reaction. The burning occurs in a reaction zone 10 whichpropagates upward through the thermite charge 4. As shown in FIG. 1C,after the burning is complete the thermite charge forms a rigid hot plug12 of a metal and oxide, ceramic-like material. The heat of the reactionmay melt into the borehole wall material as shown at 14 in FIG. 1C, ormelt through the steel well casing if one is present, to form a platformor sealing component.

SUMMARY

Improvements to the plug and emplacement design of FIG. 1 are describedwhich allow tailoring the well sealing method to achieve specificperformance objectives and improve the sealing characteristics of theresulting plug.

In one aspect, a method of sealing a well is provided, comprising thesteps of:

1) forming a platform in the well by emplacing a thermite reactioncharge in the well at a location below where the well is to be sealedand igniting the thermite reaction charge to cause a thermite reaction,wherein the products of the thermite reaction are allowed to cool andsolidify so as to form a supporting structure in the well;

2) placing a main thermite reaction charge at a target plug zonelocation where the well is to be plugged such that it rests on theplatform formed in step 1); and

3) igniting the main thermite reaction charge wherein products of thereaction of the main thermite reaction charge form a plug in the well.

It will be noted that many metal/oxide thermite formulations areavailable to achieve specific objectives. The basic aluminum/iron oxideformulation is described here for purposes of example and notlimitation, it being understood that other formulations may be suitablefor specific applications.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1C illustrate charge placement, ignition and cooling phases fora prior art thermite plug emplacement and reaction well sealing method.

FIGS. 2A-2C are an illustration of a hot compaction embodiment for wellsealing using a thermite reaction, in which FIG. 2A depicts chargeplacement, FIG. 2B depicts the ignition of the thermite charge and FIG.2C depicts the cooling and mass removal phases of the method.

FIGS. 3A-3B are an illustration of a casing heating/swaging embodimentfor well sealing where a well casing is present within the well, withFIG. 3A showing a thermite charge having two layers (lower relativelylow temperature thermite layer and upper relatively high temperaturethermite layer) being placed in the well, and FIG. 3B showing the plugformed in the well after the ignition of both layers of the thermitecharge.

FIG. 4 is a schematic illustration of a thermite cylinder showing thedirection of expansion along the axis of the cylinder when the ignitionsource is placed on the bottom of the thermite cylinder.

FIG. 5 is a schematic illustration of a thermite cylinder showing anignition source located on the centerline (axis) of the thermitecylinder and resulting radial direction of expansion. The cylinder ofFIG. 5 has pre-established cleavage planes formed in the thermitecylinder to foster the radial expansion.

FIGS. 6A-6D are an illustration of an embodiment with continuous feed ofthermite into a reaction zone, with FIG. 6A showing an emplacementphase, FIG. 6B showing an ignition phase, FIG. 6C showing a progressionof the reaction zone with continuous feed of the thermite charge intothe reaction zone, and FIG. 6D showing the completion of the reactionphase and formation of a plug within the well.

FIGS. 7A-7C are an illustration of an embodiment in which a relativelylower temperature expansive thermite charge is ignited and then arelatively higher temperature thermite charge is ignited above the lowertemperature thermite charge. FIG. 7A shows the emplacement phase, FIG.7B shows the platform formation phase in which the lower temperaturethermite charge is ignited, and FIG. 7C shows the main (relativelyhigher temperature) charge ignition.

FIGS. 8A-8C shows a similar embodiment to FIGS. 7A-7C, with anadditional relatively lower temperature thermite charge located abovethe main higher temperature charge. FIG. 8A shows the emplacement phase,FIG. 8B shows the two lower temperature thermite charges after ignition,and FIG. 8C shows the main (relatively higher) charge after ignition.Both the lower and upper low temperature thermite charges are reactedand allowed to cool sufficiently to support and confine the highertemperature main charge as shown in the sequence FIGS. 8A to 8C.

DETAILED DESCRIPTION First Embodiment Applying Compressive Vertical Loadto Thermite Plug by Loading with a Weight on Top to Reduce ProductPorosity and Force it into Well Surface Irregularities FIGS. 2A-2C

In an unpressurized thermite reaction, the product (e.g., plug 12 ofFIG. 1C) is a porous matrix of metal oxide and metal. The porosityresults from entrained voids due to the charge preparation process, inwhich some porosity remains because the powders cannot be compacted totheir maximum density, and other porosity is generated by entrainedbubbles of the very small amount of gases generated in the reaction. Theporosity of the final plug material reduces its potential strength andcauses it to be permeable to fluid flow.

To reduce the porosity, we have demonstrated that by loading the top ofthe thermite charge during ignition and burning with a static mass (suchas a solid steel cylinder having a mass, for example of between 500kg-1,500 kg, or other heavy object of roughly similar density) it will‘hot press’ the plug formed during the reaction process, reduce itsporosity, and press the thermite reaction material more firmly into thesurrounding medium. To further reduce porosity of the final product,lower melting point oxides or eutectic materials (such as calcium oxide)can be added to the thermite reactants in the thermite charge to reducethe product melt temperature and maintain it in liquid form for a longerduration. Of course, the exact weight of the static mass that is optimalmay depend on particular applications, such as for example the size ofthe well bore, the length of the desired plug sealing zone, the mixtureused in the thermite reaction charge, and other factors.

This embodiment is shown in FIGS. 2A-2C. In FIG. 2A, a well sealingapparatus is shown in the form of a thermite reaction charge 4 having acylindrical body sized to fit within a well 100, an igniter 3 for thethermite reaction charge 4, and a heavy mass 22 in the form of a solidsteel cylinder or the like applying a massive load by means of gravityto the thermite reaction charge 4. The thermite reaction charge 4 isseparated from the heavy mass 22 by means of a separator 20, which maytake the form of an insulator of any suitable material. A means 5, suchas a wireline, drill pipe, or any other conventional apparatus known inthe art is used for raising and lowering objects into the well. Themeans 5, e.g., wireline, is connected to the heavy mass 22 and lowersthe heavy mass 22, thermite reaction charge 4, separator (insulator) 20and igniter 3 as a unit into the well. Alternatively, the heavy mass canbe lowered after the thermite reaction charge has been placed into thewell at the desired location.

The igniter 3 may be of electrical in nature and a wire for the igniteris not shown, it being understood that any suitable chemical, electricalor pyrotechnic igniter could be used. The details of the igniter arewell known by persons skilled in the art, and are not particularlyimportant. The separator 20 allows the means 5 for raising and loweringto remove the heavy mass 22 from the well after ignition and burning ofthe thermite reaction charge within the well as shown in FIG. 3. In FIG.2A, the bore of the well 100 is plugged with a suitable bridge plug 2which could be made of concrete, aggregate, or other material so thatwhen the thermite reaction charge 4 is lowered into the well it rests onthe plug 2 and the full weight of the heavy mass 22 is applied directlyto the thermite reaction charge 4.

The method for sealing the well in FIG. 2A-2C is as follows. First, athermite reaction charge 4 is lowered into the well at a location wherethe well is to be sealed. A lower support (e.g., backfill or a bridgeplug platform 2) for the thermite reaction charge is provided at thelocation, and the platform 2 can be lowered or otherwise formed in thewell prior to lowering the thermite reaction charge; alternatively thebridge plug can be included as part of the thermite reaction chargeassembly lowered into the well and formed in-situ, for example using thetechniques of FIG. 7A-7C and described subsequently.

The method continues with applying a heavy mass load to the thermitereaction charge at the location, as shown in FIGS. 2A and 2B by means ofthe massive cylinder 22 resting on the thermite reaction charge 4 whileit is supported from below.

The method continues with a step of igniting the thermite reactioncharge 4 and conducting a thermite reaction in the thermite reactioncharge while the heavy mass load is applied to the thermite reactioncharge, as shown in FIG. 2B. The thermite reaction forms a plug whichexpands outwardly under load pressure from the heavy mass as thereaction occurs. This outward expansion is indicated by the arrows inFIG. 2B. The reaction continues until all the fuel in the thermitecharge is exhausted, all the while the load from the heavy mass isapplied to the thermite reaction charge 4. As shown in FIG. 2C, theresulting plug 12 is formed in the well, with the plug sufficiently hotthat it melts portions of the surrounding formation 1 as indicated by14, resulting in the plug 12 sealing the well. The means for raising andlowering 5 is then activated to raise the heavy mass 22 (and anyremnants of the separator 20) from the location where the plug 12 isformed.

The addition of a diluent to the thermite charge 4, such as metal oxidesor eutectic materials, is optionally performed so as to lower themelting point of the plug 12 and prolong the time when the plug 12 is ina liquid or viscous state. This assists in insuring that the plug 12 ispressed firmly into the surrounding formation 1. Furthermore, thecompressive load from the heavy mass 22 during burning of the thermitecharge 4 reduces the porosity of the plug 12 and helps ensure againstescape of gasses or other material from the well below the location ofthe plug 12.

Second Embodiment Diluting the Stoichiometric Thermite Metal Fuel/OxideMix to Achieve Specific Design Objectives, Including Layered ThermiteCharges FIGS. 3A-3B

The stoichiometric mixture of red iron oxide (Fe₂O₃) and aluminum powderis approximately 3:1 by mass, respectively. In this mix ratio, underatmospheric conditions, the reaction is relatively fast, violent, anddifficult to contain. It produces a large amount of thermal energy andreaches peak temperatures of nearly 3000° C., hence its use in fieldwelding and demolition.

For the purpose of sealing a well, however, the reaction must becontrolled in order to contain the reaction products and form amonolithic plug material. Diluents and/or additives to the base mixturecan be used to control the burn rate, peak temperature, and mechanicalproperties of the final plug. For instance, diluting the aluminum/ironoxide thermite formula with aluminum oxide (which is also a product ofthe reaction), moderates the reaction, and slows the reaction down to arate that allows total containment of the thermite reaction with verylittle (gas) pressure generation. While stoichiometric aluminum/ironoxide thermite reaches a nominal peak temperature of 2965° C., by addingto the original mixture mass an additional 75% by mass aluminum oxidepowder, the peak reaction temperature can be controlled to less than1700° C. and still sustain combustion. Dilutions greater than thispercentage cannot sustain the thermite reaction, hence 75% by mass isconsidered an upper practical limit to the amount of dilution. Thediluted thermite reaction charge results in a slow, controlled reactionvelocity, as low as 0.1 cm/sec, as compared to the raw/undilutedthermite mixture burn velocity of 10 to 100 cm/sec. We have appreciatedthat slow, controlled thermite reactions resulting from dilution of thethermite reaction charge at lower temperatures are desirable for wellsealing applications, and can be adapted into various thermite reactioncharge designs for well sealing. A burn velocity of approximately 1cm/sec is considered suitable for some applications in well sealing.

In one example, this dilution feature enables design of a thermite plugwith a relatively cooler lower section that reacts first and heats upthe well casing to a plastic but not molten state. The lower, coolerplug can be designed such that it will expand radially and will swagethe well casing outward to thereby fill the annular gap between thecasing and the borehole/formation wall. Then, in a second phase of thethermite reaction, an upper, relatively hotter thermite reaction chargeignites and melts through the casing and into the rock/formation wall.The cooler lower section prevents the molten material from therelatively hotter upper plug section from flowing or falling down intothe annular void between the well casing and the formation wall, whichwould negate its sealing role.

An example of this embodiment is shown in FIGS. 3A and 3B. FIG. 3A showsa well 100 having a casing 30 separated from a borehole wall 31 in aformation 1, with an annular gap 33 separating the borehole wall 31 andthe casing 30. A plug or platform 2 is placed in the well at thelocation where the well is to be sealed. A thermite reaction charge 4 islowered into the well, e.g. by means of the wireline or drill pipe 5 andplaced on the upper surface of the platform 2.

The thermite reaction charge 4 includes at least two layers of thermitereaction charge including a first relatively lower reaction temperaturelayer 40 and a second relatively higher reaction temperature layer 42.The first layer 40 is in the form of a thermite reaction material, e.g.,powdered mixture of aluminum and iron oxide, which has been diluted byaddition of one or more additives, e.g., aluminum oxide, to moderate anexothermic reaction produced by the thermite reaction material 40 whenit is ignited. The moderating of the exothermic reaction is designed tolower the reaction temperature and reaction velocity within the thermitereaction material in the layer 40 from what they would otherwise bewithout the one or more additives. In this example, the purpose of themoderation is to heat the well casing 30 to a plastic temperature suchthat radial expansion of the thermite charge during burning causes thecasing 30 to expand radially and essentially swage against the rockformation 1 and close the annular gap 31. This is shown in FIG. 3B.After ignition (by means of the igniter 3 at the lower end of the layer40), the thermite reaction progresses upwardly within the layer 40 andthe charge in the layer 40 expands radially outwardly to progressivelyswage the casing 30 against the rock wall in the formation 1, as shownat 32 in FIG. 3B.

When the thermite reaction has progressed to the top of the lower layer40, the upper layer 42 of relatively higher reaction temperaturethermite charge (for example undiluted aluminum and iron oxide powder)is ignited and the upper layer burns at a hotter temperature so as tomelt the casing as indicated at 34 in FIG. 3B and the adjacent region ofthe rock formation 1.

Accordingly, in a first aspect of this embodiment, a method of sealing awell is disclosed, comprising the steps of: lowering a thermite reactioncharge 40 into the well at a location where the well is to be sealed,wherein the thermite reaction charge 40 lowered into the well has beendiluted by addition of one or more additives to moderate an exothermicreaction produced by the thermite reaction charge when ignited, i.e.,substantially lowering the reaction temperature and reaction velocitywithin the thermite reaction charge from what they would otherwise bewithout the one or more additives to meet a specific design objectivefor the sealing of the well; and igniting the thermite reaction charge(by means of igniter 3), the thermite reaction charge burning so as toform a plug in the well.

In this embodiment, the one or more additives/diluents may take the formof a metal oxide. Other additives could be used, for example asdescribed in the article of Orru et al. cited in the Background sectionof this document. The thermite reaction charge is preferably diluted byan amount of between 5 and 75 percent by mass. For example, the thermitereaction charge is diluted by addition of aluminum oxide by up to 75percent and the reaction velocity of the thermite material is reduced toat or below 1 cm/second.

In another aspect, a method of sealing a well has been described,comprising the steps of: a) lowering a thermite reaction charge into thewell at a location where the well is to be sealed (FIG. 3A), thethermite reaction charge comprising at least two layers of thermitereaction charge including a first relatively lower reaction temperaturelayer 40 and a second relatively higher reaction temperature layer 42,b) wherein the first layer 40 comprises a thermite reaction materialwhich has been diluted by addition of one or more additives to moderatean exothermic reaction produced by the thermite reaction material whenignited, the moderating comprising lowering the reaction temperature andreaction velocity within the thermite reaction material from what theywould otherwise be without the one or more additives; and c) ignitingthe first and second layers of the thermite reaction charge. It will benoted that in the example of FIG. 3A, the first layer 40 is ignited byan igniter 3 installed in the thermite reaction charge specifically forthis purpose, and the second layer 42 is ignited by the burning of thefirst layer reaching the lower edge of the second layer.

This method can include the step of placing a platform (2, FIG. 3A) intothe well below or at the location where the well is to be sealed andplacing the thermite reaction charge 40/42 onto the platform. As shownin FIG. 3A, the first layer 40 is positioned below the second layer 42,and the second layer 42 is ignited after the first layer 40 is ignited.

In this method, the well may further include a casing (30), and ignitionof the first layer 40 causes the casing 30 to be swaged outwardly intocontact with a formation 1 surrounding the casing 30.

In yet another aspect, a method of sealing a well is disclosed, the wellhaving a casing 30 and a borehole wall 31, the casing separated from theborehole wall 31 by an annular gap 33 comprising the steps of: a)forming a swage at a first location in the well by igniting a dilutedthermite material (layer 40) lowered into the well proximate the firstlocation so as cause the casing to heat to a plastic but not moltenstate and expand the plastic casing 30 against the borehole wall 31 andthereby close the annular gap 33 (see FIG. 3A), and b) igniting a secondthermite material 42 above the first location to melt the casing andsurrounding borehole wall and form a plug in the well, as shown in FIG.3B.

In still another aspect, a well sealing apparatus has been described inFIG. 3A including a) a thermite reaction charge 40/42 having acylindrical body sized to fit within a well, the thermite reactioncharge including a first relatively lower reaction temperature layer 40and a second relatively higher reaction temperature layer 42; and b) anigniter 3 for the relatively lower reaction temperature layer. Theapparatus may further include a plug or platform 2 placed in the wellbelow the thermite reaction charge. As shown in FIG. 3A, the firstrelatively lower reaction temperature layer 40 is positioned below thesecond relatively higher reaction temperature layer 42.

A further example of this embodiment showing two thermite reactioncharges with different reaction temperatures, separated by an insulatinglayer, is illustrated in FIGS. 7A-7C and will be described subsequently.

A further example of this embodiment showing the main high temperaturethermite charge confined by one low temperature expanding charge below,and another low temperature expanding charge above the main charge, isillustrated in FIGS. 8A-8C and will be described subsequently.

A further example of this embodiment is to load the upper hightemperature plug 42 with a heavy mass to compress the reacted charge,reduce its porosity, and press the reaction products into the boreholewall, in accordance with the teachings of FIGS. 2A-2C.

Third Embodiment Designing the Thermite Ignition Geometry to AchieveThermite Product Expansion in a Desired Direction FIGS. 4, 5, 7A-7B,8A-8B

Tests of diluted thermite mixtures have shown that, when unconstrained,the thermite expands in the direction of reaction propagation. Forexample, as shown in FIG. 4, a cylindrical plug of thermite 4 ignited atits lower end by means of an igniter 3 will expand in the verticaldirection along the axis α of the plug 4 and increase in length by asmuch as 10-20%, with very little increase in diameter since the reactionoccurs as a planar front proceeding along the axis of the cylinder.

We have appreciated that for well sealing applications it is desirableto have the thermite expand radially outward. To achieve this, thecylindrical plug of thermite 4 is ignited by a hot wire (or othersuitable igniter 3) running essentially along the center axis α of thethermite plug 4 as shown in FIG. 5. With this design, the reactionproceeds radially from the centerline of the thermite plug 4 andincreases the diameter of the cylinder, not its length. For the plug toexpand radially, slippage/cleavage planes 60 (i.e., cuts) are formed inthe thermite material prior to combustion (i.e., at the time ofmanufacture or assembly of the thermite charge) to allow for radialexpansion as indicated at 62, since the compacted thermite hassufficient tensile strength to counteract radial expansion withoutslippage/cleavage planes. The cleavage/slippage planes are formed in anysuitable manner in the thermite material, such as by means of a slittingsaw, or preforming the thermite charge in pieces to produce the desiredconfiguration.

This degree of control in the direction of thermite expansion allowsdesign of sections of the thermite charge in the form of a cylindricalplug that expand radially to fit tightly inside the well casing (using alinear ignition source on the centerline of the plug), while anothersection of the thermite charge could be ignited as shown in FIG. 4 toreact in a planar direction and result in a longer plug.

An embodiment of this design could take the form of a modification ofthe thermite reaction charge of FIG. 3A in which the lower temperaturelayer 40 has an igniter positioned along the center axis of the layer 40(in the manner shown in FIG. 5), such that when the lower temperaturelayer 40 is ignited the reaction proceeds in a radial direction so as tofacilitate expansion of the thermite charge in the lower layer 40against the casing 30 and swaging of the casing against the boreholewall 31 as shown in FIG. 3B at 32. The reaction of the thermite chargein the upper region of the lower layer 40 causes ignition of the upperlayer 42. In this embodiment, the thermite charge in the lowertemperature layer 40 is fitted with slippage/cleavage planes 60 as shownin FIG. 5 so as to facilitate the radial expansion of the thermite inthe lower layer against the well casing and the performance of theswaging operation.

A second example of this embodiment would be to configure the thermitereaction charge 4 of FIG. 2A with an igniter 3 positioned along thecentral or vertical axis of the thermite charge 4 and providingslippage/cleavage planes in the thermite charge as shown in FIG. 5.

A third example of this embodiment is to configure the thermite chargeof FIG. 1A with an axially located igniter 3 extending the entire lengthof the thermite charge 4 with slippage/cleavage planes 60 (FIG. 5)formed in the thermite charge 4.

A fourth example of the design of FIG. 5 would be to incorporate thecentrally located igniter in the thermite charge 80 of FIG. 7A. Inessence in this embodiment the thermite plug includes a first portionwhich has the axially located igniter to trigger radial expansion of thethermite material (FIG. 5), and a second portion which has an igniterdesigned to trigger planar expansion (FIG. 4).

In any of these embodiments, the thermite reaction charge which isignited by the igniter may take the form of a thermite reaction chargediluted so as to reduce the exothermic reaction temperature and/or slowthe reaction speed below what it would otherwise be without the additionof the diluents. For example the thermite reaction charge could take theform of a thermite reaction charge diluted by between 5 and 75% by masswith aluminum oxide, silica, calcium oxide, or other metal oxide.

To summarize, in this embodiment a thermite plug for a well is describedwhich includes a thermite reaction charge formed as a generallycylindrical body of length L and a longitudinal axis α (FIG. 5); and anigniter 3 (FIG. 5) for the thermite material, wherein the igniter 4 ispositioned axially and extending substantially the length L of thegeneral cylindrical body along the longitudinal axis α to trigger anexothermic reaction in the thermite reaction material propagatingsubstantially from the center of the cylindrical body outwardly in aradial direction.

The thermite plug preferably includes two or more slippage/cleavageplanes 60 formed in the thermite reaction charge designed to promotingradial expansion of the thermite reaction charge during combustion. Asshown in FIG. 7A and described below, the thermite plug could include afirst section 80 having the thermite reaction charge and igniter 3 asrecited above, and a second section 84 in the form of a second thermitematerial and a second igniter 3′ disposed to trigger an exothermicreaction propagating substantially in the axial direction.

Another example, and perhaps a preferred example of this embodiment isshown in FIGS. 7A-7D. This example features a relatively low temperatureexpansive thermite plug is used to support relatively hotter thermitecharge above.

Thermite charges need to be supported in the well prior to ignition.This would normally be accomplished by installation of a bridge plug orplatform (item 2 in FIGS. 1A, 2A, 3A, and 6A) or backfilling the wellwith cement or granular material prior to thermite charge emplacement.

To simplify the emplacement operation, the expansive nature of lowertemperature thermite charges can be exploited to form a platform plugwithout the expense of backfill or bridge plugs. A lower temperatureexpansive plug, contained in an expandable metal cylinder (for example,a pleated thinwall metal cylinder) is first set off below the maincharge, allowed to cool to form a platform with adequate strength, thenthe main thermite charge is ignited above the platform.

This embodiment will now be described in conjunction with FIGS. 7A-7D.In this embodiment a plug for sealing a well includes a first thermiteplug 80 having an igniter 3. The plug 80 includes a thermite reactioncharge such as a mixture of aluminum and iron oxide. The plug 80includes an upper surface 81. An insulating block 82 is provided havingupper and lower surfaces, the lower surface of the insulating block isproximate to the upper surface 81 of the first thermite plug 80 as shownin FIG. 7A. A second thermite plug 84 is also provided having an igniter3′. The second plug 84 includes a thermite reaction charge and a lowersurface 85. The lower surface of the second plug 84 is positionedproximate to the upper surface of the insulating block 82. The thermitereaction charge in the first plug 80 may be diluted by between 5 and 75%by mass with a metal oxide, alumina, silica or the like.

The first plug 80 includes an expandable metal jacket 88 having pleatsor folds which allow the plug 80 upon ignition to expand radiallyagainst the walls of the bore and provide a platform supporting the maincharge in the second thermite plug 84. To facilitate this radialexpansion, the igniter 3 for the first thermite plug is positionedwithin the plug 80 along the center axis (see FIG. 5).

The insulating block 82 is provided so as to enable the first plug 80 tobe ignited, expanding the first plug 82 to expand against the walls ofthe bore (see FIG. 7B) and then cooled, while preventing ignition of thesecond or upper plug 84.

After the lower plug 80 has been ignited, combustion proceeds and thenafter completion the plug is allowed to cool, forming a lower plug 12 inFIG. 7C. Then, the igniter 3′ for the upper or second plug 84 isactivated and a thermite reaction occurs in the second plug 84. Thesecond plug 84 melts the walls of the bore or formation 1 and forms asecond, solid plug 12′. The first plug 12 acts as a bridge orsupport/platform for the second plug 84/12′.

Thus, in one embodiment of FIGS. 7A-7C the first thermite plug 80includes a thermite reaction charge having a relatively cooler reactiontemperature and wherein the second thermite plug 84 includes a thermitereaction charge having a relatively hotter reaction temperature. Theigniter 3′ for the second thermite plug 84 is positioned along thebottom surface of the second thermite plug. However, in an alternativeconfiguration it would be possible to form the igniter for the secondthermite plug 84 along the central axis (see FIG. 5), for example in thesituation where it is desired to form a swage in a well having a wellcasing in accordance with the teachings of FIGS. 3A and 3B.

Another embodiment uses the expansive characteristics of the lowtemperature plug to confine, from above and below, the high temperaturemain thermite charge. In FIG. 8A-8C three thermite charges are used. Thelower plug 80 is a low temperature expanding plug and forms thestructural platform for the assembly as previously described and shownin FIG. 7A-7B. Simultaneously or shortly after the lower plug hasreacted, the upper low temperature expanding charge 86 is ignited. Oncethe upper and lower plugs 86, 80 have completed their reactions, (seeFIG. 8B) the middle higher temperature plug 84 is ignited and itsreaction temperature and pressure confined to the zone between the upperand lower plugs. See FIG. 8C. Note that the upper and lower plugs 86, 80both have a centrally placed igniter 3 as in the embodiment of FIG. 5.The upper plug 86 is separated from the middle plug 84 by means of aninsulator 82.

It will be further appreciated that we have described in FIGS. 7A-7C amethod for sealing a well, comprising the steps of: a) lowering into thewell a plug comprising a first thermite plug 80 having a igniter 3, athermite reaction charge and an upper surface; an insulating block 82having upper and lower surfaces, the lower surface of the insulatingblock proximate to the upper surface of the first thermite plug, and asecond thermite plug 84 having an igniter 3′, a thermite reaction chargeand a lower surface, wherein the lower surface of the second plug ispositioned proximate to the upper surface of the insulating block; b)igniting the first thermite plug 80 so as to cause a thermite reactionin the first thermite plug, the first thermite plug expanding so as toform a plug in the well (FIG. 7B); and c) subsequently to step b)igniting the second thermite plug 84.

It will be further appreciated that we have described in FIGS. 8A-8C amethod for sealing a well, comprising the steps of: a) lowering into thewell a plug comprising a first thermite plug 80 having an igniter 3, athermite reaction charge and an upper surface; an insulating block 82having upper and lower surfaces, the lower surface of the insulatingblock proximate to the upper surface of the first thermite plug, asecond thermite plug 84 having an igniter 3′, and thermite reactioncharge and a lower surface, wherein the lower surface of the second plugis positioned proximate to the upper surface of the insulating block,and a third thermite plug 86 having an igniter 3, a thermite reactioncharge and an upper surface; a second insulating block 82 having upperand lower surfaces, the upper surface of the second insulating blockproximate to the lower surface of the third thermite plug 86; b)igniting the first thermite plug 80 and third thermite plug 86 so as tocause a thermite reaction in the first and third thermite plugs, thefirst and third thermite plugs expanding so as to form plug in the welland confine the second plug (FIG. 8B); and c) subsequently to step b)igniting the second thermite plug 84.

In one possible variation, the thermite reaction charge in the firstthermite plug (FIGS. 7A, 8A, item 80) takes the form of a thermitereaction material which has been diluted by one or more additives tomoderate an exothermic reaction produced by the thermite material whenignited, i.e., to lower the reaction temperature and reaction velocitywithin the thermite material from what they would otherwise be withoutthe one or more additives. As an example, the thermite reaction materialin the first thermite plug has been diluted by an amount of between 5and 75 percent by mass by addition of a metal oxide, silica, aluminumoxide, calcium oxide, etc. to the thermite reaction material. The thirdthermite plug 86 may also be diluted in a similar fashion.

It will further be understood that we have described a method forsealing a well, comprising the steps of: forming a platform in the wellby means of ignition of a first thermite plug 80 lowered into the well(FIG. 7A, 7B); and subsequently igniting a second thermite plug 84 at aposition above the location of the platform (FIG. 7C). In oneembodiment, the first thermite plug 80 is surrounded by an expandablemetal package 88 (FIG. 7A). In this embodiment the first thermite plug80 includes a thermite reaction material having a reaction temperaturesubstantially less than the reaction temperature of the second thermiteplug 84. Another embodiment (FIG. 8A-8C) includes a third relatively lowtemperature expanding plug 86 on the top of the assembly, which isignited simultaneously with the lowest plug 80 or shortly thereafter,forming a sealing plug to confine the subsequent reaction of the mainhigh temperature plug 84.

Fourth Embodiment Continuous Feed of Thermite Charge into Reaction ZoneFIG. 6A-6D

A thermite charge package has to be smaller in diameter than thewellbore to allow insertion of the thermite charge to a desired depth.The compacted charge package also has a finite gas filled porosity sinceit cannot be pressed to its theoretical maximum density. The plugresulting from a thermite cylinder of a specific height will be shorterthan its starting size by as much as 25% depending on the charge andproduct densities. This limits the amount of energy and material thatcan be placed in a defined or target plug zone within the well.

However, these drawbacks can be overcome by means of a tall cylinder ofthermite which is placed in the plug zone and ignited from the bottom.The thermite charge will consume itself and continuously feed thethermite reaction charge in the cylinder into the combustion zone.Furthermore, if the thermite cylinder has been diluted such that thelinear reaction rate is slower than the freefall velocity of thecylinder, the reaction will be confined to the bottom of the cylinderand not accelerate vertically up the bore of the well. This design, oneembodiment shown in FIGS. 6A-6D, enables emplacement of large volumes ofthermite material into a defined plug zone. In particular, with thisdesign much more thermite material can be delivered to the plug zonethan would be possible with a charge only as tall as the plug zoneitself. Hence, this design produces large amounts of energy in acontrolled fashion at the desired location in the well for forming aplug.

As a variation of this method, the thermite cylinder could beconstructed in two or more layers, including a first relatively lowerreaction temperature layer and a second relatively higher reactiontemperature layer, in accordance with the design of FIG. 3A. This designwould be suitable for example in the situation where the well boreincludes a casing as show in FIG. 3A and one wishes to design a swagefor the casing as shown in FIG. 3B and explained above.

With reference now to FIG. 6A, a thermite plug for a well is shown inthe form of a thermite reaction charge 4 having a generally cylindricalbody with length L, a longitudinal axis α (not shown, but see FIG. 5)and an upper end and a lower end 76, 78, respectively. An igniter 3 forthe thermite reaction charge 4 is positioned proximate to the lower end78 of the cylindrical body. The well has a target plug zone 70 having alongitudinal extent indicated by the bracket substantially less than thelength L of the cylindrical thermite reaction charge 4, as shown in FIG.6A. FIG. 6A shows the placement of the thermite plug 4 into the well bymeans of a wireline 5 or other suitable means. The well includes a plugor platform 2 below the target plug zone 70 on which the thermitereaction charge 4 rests.

FIG. 6B illustrates the ignition of the thermite reaction charge 4 bymeans of the igniter 3. The ignition of the charge results in a reactionor combustion zone 10. By means of gravity, and the consumption of thethermite material, the cylindrical charge 4 continuously feeds athermite reaction material into the reaction zone 10. This is againillustrated in FIG. 6C, showing the progression of the reaction zone 10upwards into the cylinder, or, equivalently, the continuous feed ofthermite reaction material into the reaction zone. The expansion of thethermite charge melts the wall of the formation 1 as indicated at 14 andforms a plug in the well. As shown in FIG. 6D, the reaction hasproceeded to completion by the burning of the thermite reaction chargeat the upper surface of the cylinder 76. The resulting plug 12completely fills the well and melts the surrounding formation 1 asindicated at 14 along the entire length of the target plug zone 70,forming a seal for the well.

An additional example of this embodiment is to load the charge 4 with amass 22 as shown in FIG. 2A, providing additional downward force to thethermite charge 4 in the reaction zone 10 of FIG. 6C.

Accordingly, in one aspect of this embodiment, a method of sealing awell has been described comprising the steps of a) lowering a cylinderof thermite reaction charge (4) into a well proximate to a locationwhere the well is to be plugged (FIG. 6A), b) igniting the thermitematerial, the ignited thermite material forming a reaction zone (FIG.6B), and c) continuously supplying additional thermite reaction chargefrom the cylinder to the reaction zone after performing the ignitionstep (FIGS. 6C and 6D).

As shown in FIG. 6B, preferably the cylinder has an upper and a lowerend, and wherein the igniting step b) comprises igniting the lower endof the cylinder.

Furthermore, in one preferred embodiment the thermite reaction charge 4has been diluted by one or more additives to moderate an exothermicreaction produced by the thermite material when ignited, the moderatingcomprising lowering the reaction temperature and reaction velocitywithin the thermite material from what they would otherwise be withoutthe one or more additives.

In one variation, the thermite reaction charge 4 could be formed as twoor more layers including a first relatively lower reaction temperaturelayer and a second relatively higher reaction temperature layer inaccordance with the teachings of the embodiment of FIGS. 3A and 3B.

Another variation is to use the continuous feed thermite plug 4 as thehot plug 42 as shown in FIG. 3A, to increase the amount of energy andmaterial deposited in the plug zone.

Still further variations and modifications from the illustratedembodiments are of course possible within the confines of the presentinvention. All questions concerning the scope of the invention are to beanswered by reference to the appended claims.

1. A method of sealing a well, comprising the steps of: 1) forming aplatform in the well by emplacing a first thermite reaction charge inthe well at a location below where the well is to be sealed and ignitingthe first thermite reaction charge to cause a thermite reaction, whereinthe products of the thermite reaction are allowed to cool and solidifyso as to form a supporting structure in the well; 2) placing a mainthermite reaction charge at a target plug zone location where the wellis to be plugged such that it rests on the platform formed in step 1);and 3) igniting the main thermite reaction charge wherein products ofthe reaction of the main thermite reaction charge form a plug in thewell sealing the well.
 2. The method of claim 1, wherein the firstthermite reaction charge includes an expandable metal jacket havingpleats which allow the products of the thermite reaction charge toexpand radially.
 3. The method of claim 1, wherein the first thermitereaction charge has a central axis and an igniter positioned along thecentral axis.
 4. The method of claim 3, further comprising the step ofplacing an insulating block between the first thermite reaction chargeand the main thermite reaction charge.
 5. The method of claim 1, whereinthe first thermite reaction charge has been diluted by an amount ofbetween 5 and 75 percent by mass by addition of a metal oxide, silica,aluminum oxide or calcium oxide.
 6. The method of claim 1, wherein themethod further comprises the step of placing a second thermite reactioncharge above the main thermite reaction charge, and igniting the secondthermite reaction charge before igniting the main thermite reactioncharge thereby forming a sealing plug to confine the subsequent reactionof the main thermite reaction charge.
 7. A method for sealing a well,comprising the steps of: lowering an assembly comprising a lowerthermite reaction charge, a middle main thermite reaction charge, and anupper thermite reaction charge into the well to a location where thewell is to be sealed; igniting the lower and upper thermite reactioncharges wherein the products of reaction of the lower and upper thermitereaction charges form upper and lower plugs in the well, andsubsequently igniting the main thermite reaction charge wherein theproducts of reaction of the main thermite reaction charge form a thirdplug in the well confined between the upper and lower plugs.
 8. Themethod of claim 7, wherein the lower thermite reaction charge and upperthermite reaction charges are separated from the middle main thermitereaction charge by an insulating block.
 9. The method of claim 7,wherein the lower and upper thermite reaction charges are containedwithin an expandable metal jacket having pleats.
 10. The method of claim7, wherein the upper and lower thermite reaction charges are ignitedsimultaneously.
 11. The method of claim 7, wherein the upper thermitereaction charge is ignited after ignition of the lower thermite reactioncharge and wherein the main thermite reaction charge is ignited afterignition of the upper thermite reaction charge.